Rotary hearth furnaces for the coking of coal and the calcining of coal or petroleum coke are well known. In such furnaces the charge is usually heated by combustion in the furnace chamber of some or all of the volatile matter there evolved and rabbles in the stationary roof are adjusted to deflect the heated charge into a central soaking pit or zone as the hearth rotates. Such furnaces are satisfactory for charge materials which produce sufficient combustible volatiles for the necessary heat and the particulate material is heated primarily by radiation but are not well suited for heating wet charges or materials deficient in combustible volatiles when the particulate material is heated primarily by convection. It is a principal object of our invention to provide a furnace for such materials, specifically culm.